Paper-making



Patented Apr. 17, 1934 UNITED STATES PAPER-MAKING Howard M. Cyr, Palmerton, Pa., assignor to The New JerseyZinc Company, New York, N. Y., a corporation of New Jersey No Drawing. Application April 17, 1933, Serial No. 666,506

11 Claims. (01. 92-721 This invention relates to the manufacture of paper, and has for its object the provision of certain improvements in paper-making. More particularly, the invention. aims to provide an improved method of incorporating zinc sulphide pigments in paper pulp stock.

When a zinc sulphide pigment is added to pa per pulp stock, with the object of incorporating the pigment in the paper, it may under certain conditions be stained and discolored during the process of paper manufacture by copper salts and the like resulting from the corrosion of the metal parts of the paper-making machinery. Thus, the copper web of the Fourdrinier machine and the copper lining of the beatersare subject to slow corrosion by the acidic materials used in the paper pulp stock. as for example paper makers alum (aluminum sulphate). In consequence of such corrosion, soluble copper compounds are present in the paper pulp stock, and these compounds react with zinc sulphide to form darkcolored substances which stain and discolor the paper. a

The present invention contemplates the incorporation of zinc sulphide pigments in paper pulp stock under such conditions as to preventresult of my experiments and investigations that the staining and discoloration can be decreased until it is inappreciable by decreasing the time of contact between the pigment and the liquor in the paper pulp stock, and likewise by decreasing the acidity of this liquor.

Based on the foregoing discoveries, the present invention involves incorporating the zinc sulphide pigment in the paper pulp stock at as short an interval as practicable before the transfer of the stock to the web-forming device of the paper-making machine. In addition, the hydrogen ion concentration of the paper pulp stock is so controlled-that its pH value is not lower than about 4.5 when the zinc sulphide pigment is incorporated-therein. If necessary, the hydrogen ion concentration of the paper pulp stock is further adjusted to a pH value not above about 5 prior to the transfer of the stock to the papermaking machine. Inthe preferred practice of copper compound. I have further 'foundas athe invention the pH value of the paper pulp stock is maintained above 5 for the greater part of the time that the zinc sulphide pigment remains in contact with the liquor of the paper pulp stock. The pH value of the stock may be controlled in any appropriate manner, as for example, by regulating the amount of paper maker's 'alum (aluminum sulphate) added thereto.

In carrying out the invention, it is now my preferred practice to effect simultaneous-control of the acidity of the liquor in the paper pulp stock, and of the duration of contact between the zinc sulphide pigment and. the liquor together with a control of the amount of copper compounds present. In this preferred practice of the invention, the incorporation of the zinc sulphide pigment in the paper pulp stock is carried out as follows:

The heater, orother appropriate mixing device used in place of a beater, is first flushed out to remove any soluble copper compounds that may be present therein. This operation may be carried out with fresh water or an alkaline solution. The paper pulp stock is then sized in the beater by the addition of alum, or other appropriate siz-- 30 ing agent, in such amount as to establish a pH value not lowerthan about 4.5. Just before dumping the stock from the beater the zinc sulphide pigment is mixed intothe stock. The stock is then diluted until its pH value is raised to about 5.0 or preferably higher, either by adding fresh water or by adding recirculated white water with adjusted pH. In cases where the zinc sulphide pigment employed, has an alkaline reaction, its

alkalinity is of assistance in facilitating the estab- 9' lishment of the contemplated pH value.- The diluted stock isthen transferred to the web-forming device of a paper-making machine, such as the Fourdrinier machine, which is preferably maintained relatively free from soluble copper compounds by flushing preparatory to use.

The incorporation of zinc sulphide pigments in paper increases the opacity of the paper'and likewise its brightness and whiteness. Due to the high refractive index of zinc sulphide pigments, 9 the opacity of papers containing them is retained when the papers are oiled or waxed or printed or calendered, which operations normally decrease to a substantial extent the opacity of both unfilled papers and papers containing fillers with a low refractive index. Furthermore, zinc sulphide pigments do not materially decrease the strength of the paper, when added in the amounts contemplated by the present invention, say from 1 to 10% by weight on the dry-weight of the cellulosic material in the paper pulp stock. On the contrary, zinc sulphide pigments tend when incorporated in paper in the amounts contemplated by the invention to render the strength of the paper more permanent, as determined by folding, Mullen or tear tests. Moreover, paper containing a zinc sulphide pigment does not deteriorate in mechanical properties so readily as do papers of the same type that do not contain a zinc sulphide pigment.

Various forms of zinc sulphide pigment may be used in paper making. Pigment zinc sulphide, consisting essentially of zinc sulphide, may be used with advantage where a high concentration of the pigment is desired. Other pigments containing or consisting in part of zinc sulphide may be used, such as the ordinary lithopones (composed of mixtures in various proportions of zinc sulphide and barium sulphate), the calcium-base lithopones (composed of mixtures in various proportions of zinc sulphide and calcium sulphate), and lithopone-like pigments (composed, for example, of zinc sulphide and an alkaline earth metal carbonate). In the appended claims, the term zinc sulphide pigment is intended to include not only substantially pure zinc sulphide in pigment form, but also ordinary lithopones, calcium base lithopones, lithopone-like pigments, and in general all pigments containing a substantial proportion of zinc sulphide.

I claim:

1. In the manufacture of paper, incorporating zinc sulphide pigment in paper pulp stock at such stage in the paper-making process that the zinc sulphide pigment is in contact with the liquor of the stock for as short a period of time as practicable.

2. In the manufacture of paper, incorporating zinc sulphide pigment in paper pulp stock, and thereafter transferring thepaper pulp stock to the web-forming device of a paper-making machine as promptly as practicable so as to reduce to a minimum the time of contact of the zinc sulphide pigment with the liquor of the stock.

3. In the manufacture of paper, incorporating zinc sulphide pigment in paper pulp stock while maintaining the liquor of the stock at a pH value not lower than 4.5 for such time as the zinc sulphide pigment remains in contact therewith.

4. In the manufacture of paper, incorporating zinc sulphide pigment in paper pulp stock while maintaining the liquor of the stock at a pH value above 5 for such time as the zinc sulphide pigment remains in contact therewith.

5. In the manufacture of paper, incorporating zinc sulphide pigment in paper pulp stock at such stage in the paper-making process that the zinc sulphide pigment is in contact with the liquor of the stock for as short a period of time as practicable, and maintaining the liquor of the stock at a pH value not lower than 4.5 for such time as the zinc sulphide pigment remains in contact therewith.

6. In the manufacture of paper, incorporating zinc sulphide pigment in paper pulp stock at such stage in the paper-making process that the zinc sulphide pigment is in contact with the liquor of the stock for as short a period of time as practicable, and maintaining the liquor of the stock at a pH value above 5 for such time as the zinc sulphide pigment remains in contact therewith.

7. In the manufacture of paper, the steps of mixing paper pulp stock with an appropriate sizing agent under such control of the hydrogen ion concentration of the liquor of the stock that its pH value is not lower than about 4.5, incorporating zinc sulphide pigment in the resulting sized paper'pulp stock, then diluting the paper pulp stock to the desired consistency for paper making with adjustment of the hydrogen ion concentration thereof to a pH value not lower than about 5, and thereafter making paper therefrom.

8. In the manufacture of paper, the steps of incorporating zinc sulphide pigment in paper pulp stock with such control of the hydrogen ion concentration that the pH value of the stock is not lower than about 4.5, .and thereafter utilizing said paper pulp stock with a pH value not lower than 5 in making paper.

9. In the manufacture of paper, the steps of incorporating zinc sulphide pigment in paper pulp stock with adjustment of the hydrogen ion concentration thereof to a pH value not lower than about 4.5, and thereafter transferring the paper pulp stock with a pH value not lower than about 5 to the web-forming device of a paper-making machine.

10. In the manufacture of paper, the steps of incorporating zinc sulphide pigment in paper pulp stock with such control of the hydrogen ion concentration that the pH value of the stock is not lower than about 4.5, the amount of zinc sulphide pigment being from 1 to 10% by weight on the cellulosic content of the pulp, and thereafter transferring the paper pulp stock with a pH value not lower than about 5 tothe web-forming device of a paper-making machine.

11. In the manufacturing of paper, the steps of mixing paper pulp stock with an appropriate sizing agent in a beater under such control of the hydrogen ion concentration that the pH value of the stock is not lower than about 4.5, incorporating zinc sulphide pigment in the resulting paper pulp stock immediately preceding its discharge from the beater, then diluting the stock to the desired consistency for paper-making with adjustment of the hydrogen ion concentration thereof to a pH value not lower than about 5, and thereafter transferring the pulp to the web-forming device of a paper-making machine.

HOWARD M. CYR. 

